This invention relates to a method and apparatus for cooking food using the heat of condensation from a condensable inert gaseous fluid that is injected directly into the interior of the food. As used herein, the term xe2x80x9ccookingxe2x80x9d includes partial cooking or pre-cooking, and is not limited to complete or total cooking. The term xe2x80x9cinjectedxe2x80x9d requires direct surface contact between the condensable fluid and the interior of the food. Fluid which is passed in and out of the food through a recirculating tube without touching the food, is not xe2x80x9cinjectedxe2x80x9d as the term is used herein.
In today""s fast-paced economy, consumers are relying more than ever on pre-packaged, prepared meals and meal items which can be made ready to eat by heating in a microwave or conventional oven for a short period of time. The phrase xe2x80x9cprepared meals and meal itemsxe2x80x9d refers to entire meals, and meal entrees, which are prepared and cooked by a manufacturer, packaged, often frozen, and sold to consumers in a form almost ready for consumption. Spurred by the high consumer demand, the quality, variety, and number of brands of prepared frozen meals and meal items have risen in tandem. Markets for prepared meals and meal items have expanded to include special child and toddler meals, restaurant meals, and hospital meals as well as typical adult meals.
One strict requirement for prepared meals and meal items is that they be totally safe for consumption. Among other things, the meals and meal items must be thoroughly cooked by the manufacturer prior to freezing and shipping. The short preparation times tolerated by the consumer, along with the uneven heating provided by microwave ovens and variations between different ovens, preclude reliance on the consumer to accomplish any part of the required cooking.
Because of uneven heating and other complications, manufacturers typically have not relied heavily on microwave ovens to accomplish the required internal cooking. More often, manufacturers rely on large, conventional hot air or impingement ovens (sometimes employing moist air) to cook the food products from the outside in. When cooking poultry and meats, especially those containing bones, the cooking times required for hot air or impingement ovens can be quite long. Manufacturers have sought to reduce this cooking time using a variety of pre-cooking techniques.
One particular challenge is to cook bone-in products such as poultry, to an extent needed to eliminate any redness in the vicinity of the bone. This requires thorough cooking of the bone, often to 180xc2x0 F. or higher. To achieve thorough cooking of the bone from the outside using a convection oven may result in excessive cooking of the surface portions of the food product and/or excessive cooking times. There is a need for a technique for cooking the bones and surrounding regions without excessively cooking the remainder of the food product.
In one pre-cooking technique, a hot gas such as air can be injected into the interior of the food using a plurality of closely-spaced injection nozzles or needles. The hot air can be injected at sufficient pressure, volume and temperature to elevate the interior of the food from a lower temperature to a desired higher temperature prior to placing the food in an oven, thus reducing the required cooking time in the oven. However, the heat capacity of air is quite low compared to the heat capacities of the solid and liquid-containing foods being heated. Accordingly, the amount of energy released by taking air from a higher to a lower temperature, and/or from a higher to a lower pressure, is low enough that a high volume of the air may be required to elevate the food temperature by any desired amount. The injection of too much hot air can cause unwanted drying of the food.
In another pre-cooking technique, a hot aqueous liquid can be injected into poultry or meat to raise its internal temperature. This technique has an advantage in that the heat capacity of the liquid being injected is much closer to the heat capacity of the food being heated. On the other hand, the quantity of liquid being injected is quite limited by the need to avoid over-saturation and/or excessive rinsing of the food.
In another pre-cooking technique, a plurality of closely-spaced, recirculating heat exchanger needles can be planted in the food, and a hot recirculating fluid (liquid or gas) can flow through the needles so that heat is transferred to the food through thin, heat-exchanger type needle walls. This technique has an advantage in that there is no direct contact between the heating fluid and the food. However, because the fluid cannot penetrate the food, the portions of food immediately adjacent to the heat exchanger walls may be heated to a greater extent than portions of the food away from the needles, resulting in uneven cooking.
There is a need or desire in the food industry for a process for cooking food from the inside which is uniform, efficient, and does not result in over-exposure of the food to a cooking fluid.
The present invention is directed to a process for cooking food from the inside which achieves the desired level of cooking using a condensable cooking fluid, which condenses from a gaseous to a liquid state while in direct contact with the food. As used herein, the term xe2x80x9ccondensable cooking fluidxe2x80x9d refers to a fluid which undergoes a phase transition, from gas to liquid, at a temperature between about 100-450xc2x0 F. at the pressure (if any) used for cooking. The heat of condensation of the fluid provides the heat that is needed to heat and cook the food. Because the heat of condensation is much larger than the amount of heat released by simply cooling a gas or a liquid from a higher temperature to a lower temperature, a much lower quantity of the condensable fluid is required, per pound of food being cooked, than would be required if the fluid did not undergo a phase transition from gas to liquid.
In accordance with the invention, the condensable cooking fluid is injected directly into the food at a plurality of (two or more) spaced apart locations, and the fluid cooks the food as it condenses inside the food. The quantity of condensable cooking fluid, per pound of food being cooked, is carefully controlled so as to heat the food from a known lower temperature to a desired higher temperature. The pressure of the fluid being injected is controlled so as to sufficiently diffuse the condensable cooking fluid within the food (i.e., away from the injection ports) to uniformly cook the food, without permitting excessive fluid to escape from the food before it condenses, and without causing excessive bleeding of flavorants such as marinade from the food. The product yield is thus maximized. The injection points or ports are spaced sufficiently close together so that the condensable fluid can diffuse and uniformly cook the food.
The process of the invention is particularly useful for the internal pre-cooking of frozen meals and meal items, including bone-in food products, with the final cooking step being accomplished by a conventional hot air or impingement oven. The process of the invention can also be used to thoroughly cook food items. The condensable cooking fluid is preferably inert to the food being cooked, and must be safe for consumption when cooled. One particularly useful condensable cooking fluid is steam. Steam is useful for the cooking of prepared meals and meal items, including larger multiple-serving meal items (turkeys, hams, roasts and the like) as well as individual meals and meal items. Condensing steam is also effective in cooking bones and surrounding regions, thus eliminating any redness in the final product. Generally, the quantity of condensable fluid used is sufficiently low so as not to materially affect the weight of the food product.
With the foregoing in mind, it is a feature and advantage of the invention to provide a process for internally cooking foods which uses a fairly low amount of condensable cooking fluid per pound of food being cooked.
It is also a feature and advantage of the invention to provide a process for internally cooking foods which performs an effective amount of cooking through direct contact between the food and an inert condensable cooking fluid, without adversely affecting the food quality.
It is also a feature and advantage of the invention to provide a process for internally cooking foods which uniformly cooks the food to a desired level, and which eliminates any redness in the vicinity of bones.
It is also a feature and advantage of the invention to provide a process for internally cooking foods which does not cause excessive escape of marinades and/or other internal flavorants from the food, thereby maximizing product yield.
It is also a feature and advantage of the invention to provide an integrated process for pre-cooking food using an inert condensable cooking fluid, and completing the cooking using a hot air or impingement oven, which results in energy savings, time savings, and improved product yield compared to current industrial cooking processes.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the drawings.